The invention relates to laser annealing of deposited layers of silicon or silicon alloys.
Deposited silicon, used in many semiconductor devices, is generally amorphous, microcrystalline, or polycrystalline. Ground boundaries between adjacent silicon grains impede current flow. If the deposited silicon is to be used in a device in which speed or current density is to be maximized, it may be advantageous to lessen the number of grain boundaries by increasing grain size.
A known method to increase grain size is laser annealing of silicon, which has been used in formation of transistors to increase grain size in the silicon channel region. In devices in which a heavily doped silicon layer is buried beneath an undoped or lightly doped silicon layer, and that dopant profile is critical to device performance, however, laser annealing has not been used. Laser annealing locally melts and recrystallizes silicon. During conventional laser annealing, dopants will diffuse from the heavily doped layer to the undoped or lightly doped layer, and the desired dopant profile will be lost.
There is a need, therefore, for a method to laser anneal a deposited silicon layer (or a layer of a silicon-rich alloy) having a dopant profile while maintaining that dopant profile undisturbed.